import java.awt.event.WindowStateListener;

class Singleton{
    private static volatile Singleton instance=null;
    private Singleton(){};
    public static Singleton getInstance(){
        if(instance==null){
            synchronized (Singleton.class){
                if(instance==null){
                    instance=new Singleton();
                }
            }
        }
        return instance;
    }
}

public class test {
    public static void main(String[] args) {
        Singleton instance=Singleton.getInstance();
    }
}
